1. Field of the Invention
The present invention relates generally to thermal printers and, more particularly, to a ribbon supply for use in thermal transfer printers.
2. Description of the Prior Art
The use of electronically controlled thermal printers has increased very rapidly over the last few years. In particular, the market for thermal label printers has shown significant improvement with users focusing on utilizing label printing, especially, bar-code labelling, to improve capital asset management, inventory control or time and attendance reporting--or to meet corporate or industry mandated labelling requirements--such as automotive AIAG, electronic EIA or retail UCC/UPC specifications. Label printers typically incorporate a media hub or supply of "peel away" labels adhered to a coated substrate wound in a rolled configuration. The media with the labels is drawn against a printing head, which, in turn, causes, by localized heating, a transfer of ink from an ink ribbon to a label.
The ink ribbon of these label printers may be supplied from an ink ribbon roll having a ribbon core about which the ink ribbon is wound. The ribbon core is formed of plastic or relatively thick cardboard and is mounted to a ribbon supply feed. The ink ribbon is drawn off the ribbon core to be sent through the printing head by a drive motor which is associated with a "take-up" roll mechanism. Preferably, a drag clutch is associated with the ribbon supply feed to prevent the ribbon core from rotating in a non-feed direction and to maintain a predetermined amount of drag on the ink ribbon during the printing process.
Several disadvantages of conventional ribbon supply feeds for these thermal label printers are apparent. For example, the drag clutch arrangements incorporated within the supply feeds are relative complex requiring a large number of moving and interengaging component parts. In addition, conventional clutch arrangements typically incorporate spring mechanisms which are subject to degradation (e.g. deformation of the torsion spring, etc. . . . ) over extended periods of use. Consequently, the level of drag applied to the ink ribbon may decrease to a level outside acceptable limits, which often undesirably affects the quality of the printed media. Furthermore, as the clutch surfaces wear, the frictional torque increases thereby changing the degree of angular rotation(s) of the supply feed.